1. Field of the Invention
The invention relates generally to a device and method for monitoring fatigue and more particularly to a device and method for monitoring a specific body part of a person for fatigue by measuring and evaluating the forces generated by that body part as it performs a series of sequential or repetitive motions.
2. Description of the Related Art
The prior art discloses various techniques for monitoring fatigue. Generally, a single muscle or a related group of muscles is monitored for fatigue. In Eskelinen, U.S. Pat. No. 5,349,963, for example, the fatigue level of a particular muscle is determined from electromyographic (EMG) signals that are measured from that muscle.
EMG signals may be employed to detect muscle fatigue while the muscle undergoes isometric- or isotonic-type testing. For isometric-type testing, electrodes are attached to a muscle being studied and the test subject is instructed to apply a constant force with that muscle while maintaining that muscle in a static position. For isotonic-type testing, electrodes are attached to a muscle being studied and the test subject is instructed to perform multiple cycles of repetitive motions with that muscle. In both types of testing, EMG signals, which are measurements of muscle output activity, are collected for fatigue analysis.
The prior art also discloses force monitoring systems that measure the amount of force generated by a muscle or group of muscles. For example, in Krugman, U.S. Pat. No. 5,579,238 and Barker et al., U.S. Pat. No. 5,745,376, the force that a user applies to a keyboard is measured. Feedback is provided to the user when excessive force is detected so that the user can reduce the force applied to the keyboard and thereby reduce the likelihood of developing repetitive stress injuries (RSI).
In Krugman, finger force is measured by way of a vibration detecting device attached to the keyboard. The signals from the vibration sensor are proportional to the force produced by the fingers. The force data is used to trigger auditory warning signals if the force exceeds a certain threshold level. In Barker et al., an initial force is compared with a secondary force. If the secondary force is larger than the initial force, the system triggers an auditory warning signal.
The present invention differs from the teachings of Krugman and Barker, in that both of these patents relate to the detection of excessive force, whereas the present invention relates primarily to the detection of decreased force characteristic of fatigue.
Because of the importance of avoiding muscle fatigue, there is a general need to provide techniques and systems for monitoring the onset of fatigue. The present invention relates to such techniques and systems, which are based on evaluating the force profile of a muscle or group of muscles.
Repetitive Stress Injury (RSI) is a general term that describes the consequences of repetitive activity, usually of the fingers, wrist, elbow or shoulder resulting in numbness, pain and an inability to work productively. The basic assumption for the pathogenesis of RSI is that muscles, which are doing repetitive work, will continue to generate force even after they become fatigued. Damage occurs when the muscles are not properly rested. Thus, the prime time to protect persons from RSI is during the time when the muscles are becoming fatigued.
Fatigue is usually manifested as a decrease in the amount of force produced over time. Most subjects who are undergoing repetitive motion during exercise (e.g. curls, leg exercises) will generate sufficient force to continue their exercise until they fatigue, after which there is a decrease in the amount of force being generated. However, in some subjects, as the muscles become fatigued, the force will increase temporarily and then decrease. In those situations, the subject responds to fatigue by changing the exercise rate, and/or other muscles are involuntarily recruited to assist the fatigued muscles. In any event, the object of the present invention is to avoid fatigue.
Subjects who have RSI are not able to generate as much force as non-afflicted subjects, nor are they able to conduct an exercise for as long a period of time. However, the degree of impairment is usually not quantifiable. Thus, the clinician is left with only subjective impressions about the improvement of the patient after surgical/clinical intervention. In a preferred embodiment, the invention provides an apparatus that can evaluate the force generated by the fingers as they perform repetitive motions. The same apparatus can be used to evaluate both impaired and normal subjects.
The apparatus is a combined hardware/software system that is useful for measuring the onset of fatigue, such as finger fatigue caused by the repetitive force of striking a keyboard. This fatigue monitoring system (FMS) is designed to record in real-time the force generated by each finger separately or together as they strike the keys repetitively until there is a decrease in force. The xe2x80x9cforce profilexe2x80x9d (i.e. the waveform of the force) over time is recorded by the apparatus to demonstrate the change in force characteristics associated with fatigue. The force profile may be characterized by evaluating any of a number of different parameters derived from the waveform, such as initial slope, rate of change of slope, peak height, width, etc. This system may also be coupled to the measurement of EMG signals recorded from the forearm and/or finger muscles that move the finger, so that the change in amplitude of the EMG signals may be correlated with the onset of finger fatigue. The software may provide a way also in which subject and/or patient data can be entered and printed out at a later time.
The invention may further provide a keyboard (regular or ergonomic) as the input device of the combined hardware/software system. The combined hardware/software system may also include a mouse, a joystick, or any other input device having finger- (or hand-) actuated keys or buttons. It should be understood that as used herein, the term xe2x80x9ckeys or buttonsxe2x80x9d contemplates other apparatus configurations as well, such as levers, switches, knobs, etc. When these input devices are included, the invention serves as an active fatigue monitor that evaluates the condition of the user from the force profile and alerts the user to rest when it determines the user has become fatigued.
The FMS is capable of quantifying finger fatigue recorded in real-time during repetitive motion of the fingers, either separately or together. In some regards, the FMS is like to a treadmill for fingers. It can be used clinically to evaluate patients, to ascertain the effectiveness of clinical intervention, pre-employment screening, to assist in minimizing the incidence of RSI at the keyboard, mouse, joystick, and to monitor effectiveness of various finger strengthening systems. In all applications, the key output measure is the force produced by the fingers. The conventional treadmill allows for a specific amount of work to be done until the person tires. Simultaneously, the person""s heart rate can be monitored. The FMS is similar in that it allows the user or the clinician to ascertain the amount of time a person can maintain a given force while conducting repetitive finger movements. During this time, EMG signals may also be collected by the FMS and recorded from muscles in a manner similar to the recording of heart rate while using a conventional treadmill.
In addition, once a clinical intervention has occurred, the onset of fatigue should be increased over that of the pretreatment condition. The FMS allows the clinician to be more objective in terms of assessing the improvement of the patient.
The FMS solves the problem of the lack of quantification of finger fatigue for subjects with various pathologies that influence their finger movements. Whether it is musicians, computer users, or any other persons repeatedly applying force sequentially with their fingers, the FMS allows a more scientific approach toward the management of RSI. At present, all repetitive stress injuries are considered similar. By using the FMS, it is possible to begin to discriminate between various clinical RSI manifestations.
Additional objects, features and advantages of the invention are set forth in the claims and the detailed description of preferred embodiments which follow.